Method and arrangement for idle adjustment of an internal combustion engine

Abstract

A method and an arrangement for adjusting the idle of an internal combustion engine are suggested wherein the idle rpm is increased when the engine is hot. A hot engine is then present when the engine temperature and the intake-air temperature have exceeded predetermined threshold values and the engine rpm has been above a limit rpm for a pregiven time.

What is claimed is: 
     
       1. A method for adjusting the idle speed of an internal combustion engine equipped with an adjusting device for adjusting the idle speed, the method comprising the steps of: detecting operating variables of the engine including engine temperature (Tmot), intake-air temperature (TANS) and engine speed (Nact);   evaluating said operating variables in a microcomputer to determine an operating state of the engine defined by an oil temperature greater than an oil temperature threshold above which an oil pressure can occur which is too low to effect an improved cooling of the engine; and,   generating a drive signal to drive said adjusting device to increase the idle speed when said operating state is determined to be present.   
     
     
       2. The method of claim 1, further comprising: determining a time duration during which the engine has been operated at an engine rpm above a limit rpm;   assuming said oil temperature threshold to be exceeded when the engine temperature, the intake-air temperature and the time duration exceed predetermined limit values.   
     
     
       3. The method of claim 2 wherein, when determining said time duration, the time duration is subtracted during which the engine was driven at an engine rpm above a limit rpm for which the engine rpm is below the load threshold so that oil can cool down. 
     
     
       4. The method of claim 2, wherein a counter value is incremented to determine an rpm criterion and decremented when there is a drop below the limit rpm. 
     
     
       5. The method of claim 4, wherein said operating state of the hot engine is determined when said counter value exceeds a predetermined limit value and the engine temperature and the intake-air temperature exceed predetermined threshold values. 
     
     
       6. The method of claim 2, wherein said operating state of the hot engine is viewed as not being reached or viewed as having been left when the engine temperature or the intake-air temperature or the time duration of exceeding the rpm limit value or the counter value drop below pregiven threshold values. 
     
     
       7. The method of claim 4, wherein the counter value is permanently intermediately stored and, after start of the engine, a start is made with said intermediately stored counter value. 
     
     
       8. The method of claim 4, wherein said counter value is set to a pregiven value including the value 0 when the control unit is taken into service for the first time or after the current supply is interrupted. 
     
     
       9. The method of, claim 1 wherein, in the idle state when the operating state of the hot engine is detected, the idle rpm is increased and, when said operating state is left, the rpm is reduced. 
     
     
       10. The method of claim 9, wherein the rpm is reduced in the next idle cycle. 
     
     
       11. An arrangement for adjusting the idle speed of an internal combustion engine equipped with an adjusting device for adjusting the idle speed, the arrangement comprising: a first measuring device for detecting the temperature (Tmot) of said engine as a first operating variable thereof;   a second measuring device for detecting the temperature (TANS) of the intake air inducted by said engine as a second operating variable thereof;   a third measuring device for detecting the rpm (Nact) of said engine as a third operating variable thereof;   a control apparatus including a microcomputer connected to said measuring devices to receive said operating variables; said microcomputer being programmed to perform the following steps: (a) reading in said operating variables;   (b) evaluating said operating variables to determine an operating state of the engine defined by an oil temperature greater than an oil temperature threshold above which an oil pressure is to be expected which is too low to effect an improved cooling of the engine; and,   (c) generating a drive signal to drive said adjusting device to increase the idle speed when said operating state is determined to be present; and,     circuit means for conducting said drive signal from said microcomputer to said adjusting device thereby actuating said adjusting device to increase said idle speed of said engine.